Tilequery: describe_tileset + tilequery tools, starting with elevation along a route #289

Problem

Some questions need data that's in Mapbox tilesets but not behind any tool in this server:

• "How high is this point?" and "How hilly is this bike route?" (terrain)
• "How tall is this building?" (Streets v8 building.height)
• "Is this spot in a park or an industrial area?" (Streets v8 landuse.class)
• "Which of our sales territories is this address in?" (a customer's own tileset)

mcp-devkit-server has a generic tilequery_tool, but a model can only use it well if it already knows the tileset id, layer names and fields. Most models outside a developer setting don't.

Proposal

1. describe_tileset_tool

Takes a tileset id and returns its layers, with field names, geometry type and zoom range, read from the tileset's TileJSON. TileJSON already carries this. For example:

• mapbox.mapbox-streets-v8: 16 layers.
  • building: height, min_height, underground, extrude
  • road: class, lane_count, bike_lane, access
  • landuse: class, type
  • natural_label: elevation_m
• mapbox.mapbox-terrain-v2: contour (ele, index), landcover, hillshade

It's cheap and cacheable, and it works on the user's own tilesets too.

2. tilequery_tool

Tilequery API: tileset, point, radius, layers, limit, geometry type. It returns only the matched features' properties and distances, not full geometry, to keep results small. Its result includes a mapboxRender.ref so the hits can go on the map.

3. Built-in notes for Mapbox-owned tilesets

A few lines in the tool descriptions for Streets v8, Terrain v2 and Traffic v1: what each is good for, and the fields TileJSON leaves out. For example, Traffic v1's TileJSON lists no fields, but its tiles carry congestion, class and structure (checked against a live tile while working on #278). With these, common questions don't need a describe call first.

4. First use case: elevation along a route

A tool built on top of the two above. It takes a directions_tool ref or a line, samples points along it against the terrain tileset, and returns:

• total climb and descent
• the highest and lowest points
• a small profile the map could chart

It's a clear gap today (this server has no elevation at all), and it pairs well with routes on the map. A single point's elevation falls out of the same work.

Open questions

• Duplication with devkit. Do we copy devkit's tilequery_tool here, move it here and keep devkit for developer and admin work, or share the code?
• On by default? Two more general tools add to tool-selection load. Off by default, at least for the hosted connector? Run the tool-selection eval (feat(evals): tool-selection eval for description routing regressions #274) either way.
• Listing tilesets. Listing a user's own tilesets needs the broader tilesets:list token permission. Leave listing to devkit, and have users name the tileset?
• Terrain precision. Vector contours come in fixed elevation steps. Check what tilequery gives on Terrain v2 versus the terrain DEM before promising elevation accuracy.
• Resource too? Claude Desktop and ChatGPT don't let the model read resources on its own, so describe has to be a tool. Should it also be a mapbox://tilesets/{id} resource for hosts that do support reading them?